Signal recording and reproducing method



April 10, 1945. G. c. szlKLAl i SIGNAL RECORDING AND REPRODUCING METHODFiled Oct. 28, 1942 HMPZ /F/EE HUD/O S/G/HL. SOURCE Snventor IKLHI 1MREMZ Gttorneg Patented Apr. 10,1945

l 'am .George C. Sziklai, Bloomington, Ind., asslgnor to RadioCorporation of America, a corporation of Delaware Application october2s, 1942, senat No. 463,610

(ci. 11s-100.1) p

8 Claims.

' This invention relates to a Signal recording and.: reproducing method.and hasfor lts principal object the provisionof a novel method ofrecording and reproducing sound electrically.

More particularly, it is an object of the present invention to providean improved method of recording and reproducing sound electrically bymeans of which high fidelity recording and reproduction may beobtained.

, Another object ofthe present invention is to provide a novel soundrecord which is durable and permanent in character.

Still another object of the present invention is to provide an improvedsound record as aforesaid which will vhave a long playing time. yet willrequire small storage space.

A further object of the present invention is to provide an improvedmethod of sound recording which will yield a plurality of identicalsound records in only one recording operation.

It is also an object of the present invention to provide an improvedmethed as afoesaid which 1s inexpensive to practice and is highlyefficient. as well as to provide an improved record which will-becomparatively lowin cost.

In accordance with this invention, a strip of conductive tape orwireisconnected to one of the terminals of an audio voltage source. theother terminal therecf being connected tn a film forming solution. Thestfip is advanced along a path such that it is brought either intocontact with or in veryclose proximity to the film forming electrolyteover a very small area of the strip. As the potential changesadielectric film of varying thickness forms on the conductive strip.'I'he strip is preferably biased beyond the audio peak voltage, so thatthe thickness of dielectric lm which forms onv the stripwill be areplicaof the frequency and amplitude of the sound. To reproduce thissound record, the coated strip may be passed through a conductive bath,`again with only a small area thereof in contact with the bath, so thatthis small portion or area acts as a condenser. The variations inthickness of the dielectric lm will cause the capacity to changecorresponding to the audio -yoltage which was used in forming the lilm.This change in capacity may be utilized to change 'the-frequencyfof anassociated reproducing cir- 'cuit to produce frequency, amplitude, o:phase modulation,depending upon the typeof reproducing circuit employed.or it may -be utilized .similarly to a condenser microphone, forexample, to vary. a suitable voltage to produce A.signal voltagesrepresentative of the sound origoperation simultaneously,

inally recorded.' If a relatively wide strip o tape is used on^which torecord, the strip may be split longitudinally after recording to providea plurality of individual, identical records. each of which may bereproduced separately. A plurality of identical records may also beproduced by subjecting a number of strips to the recording the stripsbeing arranged in side-by-side relation.

The novel features that I consider charactegistie of my invention areset forth with particularity in the appended claims. -The inven tionitself, however. both as to its organization and method of operation, aswell as additional objects and advantages thereof, will best -beunderstood from the following description of one embodiment thereof.when read in connection with the accompanyingr drawing in which Figure lis a diagrammatic view of a recording system employing the method of mypresent invention.

Figure 2 is a similar view of a reproducing system by means of which thenovel record of my invention may be reproduced, and

Figure 3 is a fragmentary sectional view of one form of my improvedrecord.

Refering more particularly to the drawing.

wherein similar reference characters designate corresponding partsthroughout. there is shown. in Flg. l, a source -I of audio signalscoupled to an amplifier 3, in turn coupled to an output transformer 5.One terminal of the secondary winding of the tansformer 5 is connectedthrough a polarizing battery l to a conductive receptacle 9 whichcontains an electrolyte il. The other terminal of the secondarywinding'of the transformer has electrical connection with a conductiveroller i3 through a resilient brush or the like l5.

A conductive strip, such as a tape or wire il, is fed from a supply reeli9 around the conductive roller i3, then down around a small dielectricvroller 2l where the strip Il is given a sharp.

substantially reverse bendof small radius,zthence around a. roller 23and on to a takeup reel 25.

The strip ll andthe electrolyte Il are of such I1 is of aluminum. andthe electrolyte I| is approxlmately a two percent aqueous solution ofborax or Vammonium borate.

so that contact therebetween will be obtainedthrough capillaryattraction and the required electrolytic action will take placeinstantaneously over only a very narrow, line-like area transversely ofthe strip i1.

It will be obvious, from the foregoing, that, as the signal potentialchanges, a dielectric iilm layer or coating 21 of varying thickness willbe formed along the length of the strip I1. The polarizing battery 1serves to appliY a bias beyond the peak audio voltage, so thatregardless of the direction in which the audio voltage swings, adielectric film of varying thickness will be formed on the conductivestrip I1. In this way, variations in signal voltage will produce adielectric coating of varying' thickness representative of the frequencyand amplitude of the sound or other signals being recorded. Obviously, anumber of parallel strips may be fed past the electrolyte Ilsimultaneously to provide a plurality of identical records which can bereproduced'or played back separately, or, if a wide strip is used, itcan be split longitudinally after recording across its entire width toprovide a plurality of identical records.

A record formed as above may be utilized in a reproducing system such asthat illustrated in Figure 2, for example. In this system there is showna grounded conductive receptacle 3| containing a conductive body 33,such as mercury. 'Ihe receptacle 3| is connected to one terminal o! atimed circuit 35 which constitutes the tank circuit of a suitableoscillator 31. The other terminal of the tuned circuit is connectedthrough a resilient brush 39 to a large conductive roller I8. The coatedstrip l1, 21 may be fed from a supply reel 43 around a roller 45, andthence down around a small roller 41 similar to the roller 2| and aroundwhich the record strip takes a sharp. substantially reverse bend ofsmall radius. From there, the strip i1, 21 passes around a roller I8 andthen is guided by a pair of rollers 49 around and in contact with alarge portion of the circumference of the conductive roller l0, and fromthere, the strip 1, 21 passes around a roller B0 toatakeupreel 4|.

As the successive, small areas of the record strip |1, 21 come intocontact with the conductive body 33, the varying thicknesses of thedielectric coating 21 will produce changes in capacity to vary thetuning of the tuned circuit 35 and thereby vary correspondingly thefrequency of the voltage supplied by the oscillator 3T. .In this way.there are set up signal voltages representative of the sound originallyrecorded. The conductive roller l0, in cooperation with that portion ci'the conductive `strip |1 between the rollers I3 and the dielectriccoating 21 therebetween i'orms a large -capacitor in series with thesmall. constantly varying, timing capacitor under the roller I1 and itshould be made so large that it will not appreciably alter the tuningprovided by the small capacitor under the roller 41. A coupling coil maycouple the oscillator circuit to suitable reproducing apparatus such asa limiter, frequency dlscrlminator, amplifier and loudspeaker, toreproduce the sound.

The speed with which the strip I1 is advanced either during recording orreproducing, and the area of contact between the advancing strip and theelectrolyte I |-or the conductive body 33, as the case may be, will varyin accordance with the highest frequency which it is desired to record.For example, with an area of exposure of approximately .003 inch alongthe length of the strip, the strip may be advanced at a rate of 100inches per minute to record up to -5000 cycles per second. With the sameexposure area, if it is desired to .record -up to 10,000 cycles persecond, the strip should be advanced at a speed of about 200 inches perminute. However, if the slower speed is preferred, the exposed areashould be only 0.0015 inch along the length of the strip. In general,exposure areas oi' from about .01 inch to about .001 inch will be foundsatisfactory for most practical purposes.

Although I have shown and described certain forms of my invention inconsiderable detail, it will be obvious to those skilled in the art thatmany other forms of the invention, as well as variations in the onesdescribed, are possible. For example, in the reproducing system of Fig.2, a second and relatively long conductive receptacle vsimilar to thereceptacle 3| but very much longer than the latter and also containingmercury or any other suitable conductive body may be substituted for thelarge conductive roller and the strip l1, 21 caused to pass therethroughin advance of the takeup reel. Thus, there will also be provided a largecapacitor in series with the small, constantly varying tuning capacitorunder the roller 41. Iny an alternative reproducing arrangement, theroller 40 or other conductive member which aids in forming the largecapacitor may be entirely dispensed with and the reels 4| and I3 made ofconductive material with which both ends of the conductive strip |1would have electrical contact. One brush corresponding to the brush 39would then engage one of the reels to connect it to one terminal of thetuned circuit 35 and` another, similar brush would have electricalcontact with the other of the reels and would also be connected to thesame terminal of the tuned circuit 35. I f the tuned circuit 35 wereconnected to only one of the reels (for example, the takeup reel 4| thenthe gradually increasing inductance i'ormedV by the portion of the stripwound thereon would choke off the higher signal frequencies. However, byconnecting the tuned circuit 35 to both of the reels 4| and |13, then,as the inductance increases on one wheel it would correspondinglydecrease on the other, but the effective inductance would remainconstant. Many other changes will, no doubt, readily suggest themselvesto those skilled in the art. I therefore desire that my invention shallnot be limited except insofar as is made necessary by. the prior art andby the spirit of the appended claims.

I claim as my invention:

1. The method of recording signals which comprises subjecting successiveportions of an electro-conductive material to the action of a secondmaterial which is adapted to react therewith chemically under theiniiuence of an electrical potential to form adielectric coating thereonwhile applying thereto avarying potential representative of said signalswhereby to form on said chemically under the iniiuence of an electricaltical signal records which comprises passing a astraavs 3 ilrst namedmaterial a dielectric coating of varytiguous, small areas oi said stripto contact said ing thickness representative oi said signals.electrolyte as said strip advances in said path, 2. The method ofrecordingsignals which comand simultaneously applying to said stripvarying prises bringing successive, small areas of an elec potentialsrepresentative of said signals whereby tro-conductive material intoreactive relation to form on said strip a continuous dielectric coatwitha second material which is adapted to react' .ing ci varying thicknessrepresentative of said therewith chemically under the influence of an`signals. electrical potential to form a dielectric coating 6. Thevinvention set forth in claim 5 .characthereon, and simultaneouslyapplying thereto terized in that said path has a substantially revarylngpotentials representative cf said signals l0 verse bend therein of smallradius, and characwhereby to form on said irst named material a terizedfurther in that said strip is brought into dielectric coating of varyingthickness represencontact with said electrolyte at said bend. tative ofsaid signals. 7.= The invention set forth in claim 5 charac- 3. Themethod of recording signals which comterized in that said strip is ofaluminum, and prises bringing successive, small areas of an elecl5characterized further in that said electrolyte is tro-conductivematerial into contact with a secconstituted by an aqueous solution cf aberate. ond material which is adapted to react therewith 8. The methodof forming a plurality of idenpotential to form a dielectric coatingthereon, strip of electro-conductive material continuously andsimultaneously applying thereto varying po- 20 along a path in theneighborhood of an electrotentials representative of said signalswhereby lyte which is adapted to react chemically with to i'orm on saidrst named material a dielectric said material under the influence of anelectrical coating of varying thickness representative of potential toform a dielectric coating on said strip, said signals. causingsuccessive, contiguous, small areas oi' said 4. The invention set iorthin claim 3 charac- 25 strip to contact said electrolyte as said stripadterized in that said areas are contiguous whereby vances in said path,said areas extending all the said coating is continuous on said rstnamed way across said strip, simultaneously applying to material. saidstrip varying potentials representative of the 5. The method ofrecording signals which comsignals whereby to form on said strip acontinuous prises passing a strip of electro-conductive maso dielectriccoating oi varying thickness representerial continuously along a path inthe neighbortative of said signals, and ilnally dividing said hood of anelectrolyte which is adapted to react strip longitudinally to therebyprovide a plurality chemically with said material under the inuoi'identical, individual records of said signals. ence oi an electricalpotential to form a dielectric coating on said strip, causingsuccessive, conas GEQRGE C. SZIKLAI.

